This invention relates to an improved cutting assembly in the form of a rotary head for a rotary lawn mower, edger, trimmer or the like. The preferred embodiments are in the form of portable hand-held type lawn mowing and edging tools wherein the cutting element is safe and in most uses and avoids the hadardous conditions created by prior art devices.
The prior art is prolix with attempts at solutions of to provide a safe, efficient and simply constructed rotary head for rotary lawn mowers, edgers, trimmers and the like. Heretofore, the rotary head, or cutting blade, of rotary lawn mowers, edgers and the like, has comprised a rotating metal knife blade which is rotated at sufficient speeds to effect cutting of grass, weeds or the like. However, such blades create hazardous conditions in that when they strike certain objects they act upon those objects in a fashion to create and project dangerous missiles which may strike the operator or individuals in the area of work.
Various attempts have been made to overcome the aforesaid hazardous conditions created with rigid type metal cutting blades of the prior art and, in particular, attempts have been made to utilize some type of flexible flail-like member which will have sufficient resiliency so as not to project impacted rocks and other objects at dangerous velocities. Most of these resilient type cutting elements of the prior art suffer a disadvantage in that mere resiliency alone is not sufficient to insure that the dangerous conditions will not be created when rotation is effected at desired cutting speeds. Further, resilient cutting members of the type represented in the prior art have no cut vegetation as well as the metal blades hereinbefore described, and have not enjoyed commercial success for this reason.
The result has been that most of the type of lawn edging and trimming around trees and the like, which would otherwise be damaged by the metal blades, must be done manually, which is both laborious and time consuming.
There is depicted and described in the following West German petty patents Nos. 6,919,841, 6,919,842, 6,919,843, 6,919,844, 6,938,265 and 7,043,648 one or more embodiments of a lawn mowing or trimming device having a disc-like head member arranged to be rotated by an electric motor, and containing a spool which is housed therein in coaxial relationship to the shaft of the motor. A length of flexible non-metallic line is coiled about the spool, whereby its free traveling end extends generally peripherally from the spool and head, and whereby such free traveling end will be swung arcuately about upon actuation of the motor to cut adjacent vegetation in the manner of a flail.
Use of the German device has revealed that, under ideal operating conditions, a length of flexible non-metallic line or string may be used to cut or trim grass and other light-weight vegetation with reasonable effectiveness. Furthermore, a cutting device of this type possesses a significant safety advantage with respect to the more conventional blade-type cutters, in that it does not cause stones or other solid objects to be discharged in the same dangerous manner, and it is almost completely incapable of causing any significant injury to persons or pets struck by the flailing cutting string. In fact, it is a reasonable statement that the German device will actuatlly cut substantially only the vegetation to which it is directed.
On the other hand, the German device is also subject to certain disadvantages of a magnitude such as to severely limit if not destroy its practical value. In the first place, although it is reasonably capable of cutting light-weight vegetation it is almost completely useless for any other task. In the second place, it will only cut such vegetation if growing relatively sparsely, and it cannot effectively handle even light-weight vegetation if encountered in a rank condition. A more serious disadvantage, however, is that, for a variety of non-obvious and complex reasons, the German device experiences a breakage rate with its cutting strings which is so high as to keep such a device from having much practical value.
It will be readily apparent from a consideration of the teachings hereinafter provided that a cutting string which is free from internal flaws or other defects will not usually break except as a result of being struck against or across a relatively immovable object. The cutting string may, of course, be formed of a metal wire or heavy strap in order to provide it with a tensile strength sufficient to resist such impact, but such a string will create substantially the same dangerous conditions which exist when the cutting element is a rigid blade or the like. Thus, the safety advantages which are present with the German device are directly derived from the same design feature which is the reason for excessive string breakage, i.e., the fact that the cutter used by the German device is a light-weight plastic cutting line having a relatively small diameter, and therefore relatively incapable of cutting any but the lightest and sparsest vegetation.
The disadvantages of the prior art, and especially the aforementioned German device, have been overcome with structures devised according to teachings contained in the aforementioned copending patent applications Ser. No. 347,997 and Ser. No. 321,580, and commercially acceptable embodiments of a vegetation cutter and the like have been proposed which are not only fully capable of cutting vegetation under most operating conditions,, but which are also fully capable of other tasks completely beyond the capabilities of the German device, such as cleaning dead leaves, trash and other such debris from along fences, walls and the trunks or stems of trees and bushes. More particularly, however, the apparatus described in these copending patent applications are capable of operation with a much lower breakage rate for their cutting strings, without any sacrifice whatsoever of the safety features and advantages hereinbefore accorded to the aforementioned German cutting device.
It is well known that there is a substantial market for good quality apparatus which can be made commercially available at a reasonable price. Accordingly, trimmer devices constructed according to the concepts and teachings set out in the aforementioned copending patent applications have enjoyed substantial commercial acceptance for the reasons hereinbefore set out. Nevertheless, it is also well known that there is a concurrent market for devices of a lesser quality if they can be made availabe at a substantially lower price. Thus, the aforementioned trimmers of the prior art continue to enjoy substantial sales notwithstanding their tendency to experience a breakage rate which is undesirable to most users of this type of equipment.
It should be understood that the replacement cost of the cutting lines for this type of trimmer is not a particularly onerous burden for the average user. Instead, it is the inconvenience of continual replacement of broken cutting lines which is the principal disadvantage, inasmuch as this requires either partial disassembly of the trimmers of the prior art or else the stubs of broken strings are required to be removed before new strings may be attached and the trimmer restored to operation.
These disadvantages of the prior art have been substantially reduced by the present invention, and novel trimming apparatus is herewith provided wherein string replacement is not only greatly facilitated but wherein the breakage rate is substantially reduced.